Beamforming (BF) is a diversity technique making the most of multi-antenna arrays. For millimeter-wave systems, e.g. 60 GHz wireless personal area network (WPAN)/wireless local area network (WLAN) systems, beamforming becomes extremely important due to the high path loss coherent to the systems. Different antenna configurations, such as sectored antennas, 1D/2D phased antenna array and the like, are capable of supporting beamforming. For 60 GHz application, a CMOS-based low-cost phased antenna array, expected to support around 30 dBi antenna gain, is regarded as the effective way to combat high path loss at 60 GHz spectrum.
Recent physical (PHY) layer standards of 60 GHz, such as Wireless HD, Wigig, and IEEE 802.11ad, all support both single carrier and orthogonal frequency division multiplexing (OFDM) transmission modes. However, from a beamforming point of view, the two transmission modes are almost not different in implementation.
Beamforming training is necessary for a pair of communication stations communicating with each other to achieve the optimum transmit antenna weight vectors (TX AWVs, also known as transmit beamforming vectors) and receive antenna weight vectors (RX AWVs, also known as receive beamforming vectors).
US Patent Application Publication US20090318091 A1 discloses a system that makes use of a concatenated training sequence for one-to-many simultaneous beamforming training. In the system, a transmitting station first generates a concatenated training sequence composed of n sub training sequences. When each sub training sequence is transmitted through a transmit antenna array including a plurality of antenna elements, a unique TX AWV is applied to differentiate the phases on these plurality of antenna elements, such that the transmitted sub training sequence has a unique beam pattern.
The transmitting station transmits this concatenated training sequence for the simultaneous training of multiple receiving stations. Based on certain metrics, such as capacity or signal-to-noise-ratio (SNR), each of these receiving stations determines an optimum TX AWV for the receiving station and feeds it back to the transmitting station.
Based on a codebook (CB) or other rules, the plurality of TX AWVs applied by the transmitting station are predetermined, and are known to the transmitting station and the plurality of receiving stations under training. Therefore, it is easy for the plurality of receiving stations to feedback their respective optimum TX AWVs.
In a typical IEEE 802.11ad dense-user conference room environment, where multiple pairs of stations need to transmit and receive data simultaneously and a personal basic service set (PBSS) control point (PCP) acts as a network coordinator (CDNT) of all stations. Since the multiple pairs of stations need to perform proactive/on-demand beamforming training, time division multiplexing access (TDMA) contention based one-by-one training method will be too time-consuming. In other words, in prior art, multiple communication pairs must perform beamforming training in different periods of time, which is time-consuming and lacks spectral efficiency.